Etymology
Advertisement
reef (v.)

1660s, "take in, roll up" (a section of a ship's sail or something like it, t reduce the extent of it), from reef (n.2). Later also in a general sense of "gather up stuff" of any kind (1836), hence the criminal slang sense of "to pick" (a pocket). Related: Reefed; reefing.

Related entries & more 
Advertisement
reef (n.1)

"low, narrow rock ridge underwater," 1580s, riffe, probably via Dutch riffe, from a Scandinavian source such as Old Norse rif "ridge in the sea; reef in a sail," literally "rib" (see rib (n.)). Also extended to the low islands formed by coral debris or to any extensive elevation of the bottom of the sea.

Related entries & more 
reef (n.2)

"horizontal section of sail rolled or folded" to reduce the area exposed to the wind, late 14c., rif (mid-14c. in rif-rope "rope used in tying down a reef"), from a Scandinavian source such as Old Norse rif "reef of a sail," probably a transferred use of rif "ridge under the sea; rib" (see rib (n.) and compare reef (n.1)). German reff, Swedish ref, Norwegian riv, Danish reb likely all are from the Old Norse word.

Related entries & more 
reefer (n.)

"marijuana cigarette," 1920s, perhaps an alteration of Mexican Spanish grifo "marijuana, drug addict" [OED]; or perhaps from reef (v.), on resemblance to a rolled sail. It also meant "pickpocket" in criminal slang (by 1935), and Century Dictionary also has it as "oyster that grows on reefs in the wild."

Reefer also was a nickname for the sailing navy's equivalent to a midshipman (1818) "because they attend in the tops during the operation of reefing" [Century Dictionary], which is the source of the meaning "coat of a nautical cut" (1878) worn by sailors and fishermen "but copied for general use in the fashions of 1888-90" [CD].

Related entries & more 
coral (n.)

general name for the hard, calcareous skeleton excreted by certain marine polyps, c. 1300, from Old French coral (12c., Modern French corail), from Latin corallium, from Greek korallion, a word perhaps of Semitic origin (compare Hebrew goral "small pebble," Arabic garal "small stone").

Originally especially the red variety found in the Mediterranean, used ornamentally, hence "red, the (red) color of coral" (mid-15c.). As an adjective, "made of coral," mid-15c. The coral-snake (1760) is so called for the red zones in its markings. Coral-reef is attested from 1745 (see reef (n.1)).

Related entries & more 
Advertisement
key (n.2)
"low island," 1690s, from Spanish cayo "shoal, reef," from Taino (Arawakan) cayo "small island;" spelling influenced by Middle English key "wharf" (c. 1300; mid-13c. in place names), from Old French kai "sand bank" (see quay).
Related entries & more 
barrier (n.)
"anything meant to obstruct entrance," early 14c., barere, from Anglo-French barrere, Old French barriere "obstacle, gatekeeper," from barre "bar" (see bar (n.1)). First record of barrier reef is from 1805.
Related entries & more 
scar (n.2)
"bare and broken rocky face of a cliff or mountain," 1670s, earlier "rock, crag" (14c.), from Old Norse sker "isolated rock or low reef in the sea," from Proto-Germanic *sker- "to cut" (from PIE root *sker- (1) "to cut") on the notion of "something cut off."
Related entries & more 
atoll (n.)
"island consisting of a strip or ring of coral around a central lagoon," 1620s, atollon, from Malayalam (Dravidian) atolu "reef," which is said to be from adal "closing, uniting." Watkins writes, "Perhaps ultimately from Sanskrit antara-, interior" (from PIE root *en "in"). The original use was in reference to the Maldives. Popularized in present form by Darwin's writings.
Related entries & more 
granny (n.)
also grannie, 1660s, according to OED, most likely a diminutive and contraction of grannam, shortened form of grandame, rather than from grandmother. The sailor's granny knot (by 1803), originally granny's knot, readily jammed and insecure, is a reef or square knot with the second part crossed the wrong way, so called in contempt because "it is the natural knot tied by women or landsmen" [Smyth, "Sailor's Word-Book," 1867]. Granny Smith apples (1895) are said to have been named for Maria Ann Smith (d. 1870) of Australia, who originated them. Granny glasses attested from 1966.
Related entries & more